From 6004badce2ad3d1e0d26f66fd48c1ed81ea5ac4c Mon Sep 17 00:00:00 2001
From: Suleyman TURKMEN <sturkmen@hotmail.com>
Date: Mon, 10 Mar 2025 15:54:01 +0300
Subject: [PATCH] ImageCollection animations

---
 modules/imgcodecs/src/grfmt_gif.cpp       |  5 +++
 modules/imgcodecs/src/grfmt_png.cpp       |  5 +++
 modules/imgcodecs/test/test_animation.cpp | 45 +++++++++++++++++++++++
 3 files changed, 55 insertions(+)

diff --git a/modules/imgcodecs/src/grfmt_gif.cpp b/modules/imgcodecs/src/grfmt_gif.cpp
index c229a45201..653b62ddc8 100644
--- a/modules/imgcodecs/src/grfmt_gif.cpp
+++ b/modules/imgcodecs/src/grfmt_gif.cpp
@@ -34,6 +34,11 @@ GifDecoder::~GifDecoder() {
 }
 
 bool GifDecoder::readHeader() {
+    if (m_frame_count > 1 /* if true, it means readHeader() was called before */)
+    {
+        return true;
+    }
+
     if (!m_buf.empty()) {
         if (!m_strm.open(m_buf)) {
             return false;
diff --git a/modules/imgcodecs/src/grfmt_png.cpp b/modules/imgcodecs/src/grfmt_png.cpp
index 5eb4a379ae..dd5ac49a63 100644
--- a/modules/imgcodecs/src/grfmt_png.cpp
+++ b/modules/imgcodecs/src/grfmt_png.cpp
@@ -249,6 +249,11 @@ void  PngDecoder::readDataFromBuf( void* _png_ptr, unsigned char* dst, size_t si
 
 bool  PngDecoder::readHeader()
 {
+    if (m_frame_count > 1 /* if true, it means readHeader() was called before */)
+    {
+        return true;
+    }
+
     // Declare dynamic variables before a potential longjmp.
     Chunk chunk;
 
diff --git a/modules/imgcodecs/test/test_animation.cpp b/modules/imgcodecs/test/test_animation.cpp
index 4e3f95013c..5bfb3dc231 100644
--- a/modules/imgcodecs/test/test_animation.cpp
+++ b/modules/imgcodecs/test/test_animation.cpp
@@ -543,6 +543,51 @@ TEST(Imgcodecs_APNG, imencode_rgba)
     EXPECT_EQ(read_frames.size(), s_animation.frames.size() - 2);
 }
 
+typedef testing::TestWithParam<string> Imgcodecs_ImageCollection;
+
+const string exts_multi[] = {
+#ifdef HAVE_AVIF
+    ".avif",
+#endif
+#ifdef HAVE_IMGCODEC_GIF
+    ".gif",
+#endif
+    ".png",
+#ifdef HAVE_TIFF
+    ".tiff",
+#endif
+#ifdef HAVE_WEBP
+    ".webp",
+#endif
+};
+
+TEST_P(Imgcodecs_ImageCollection, animations)
+{
+    Animation s_animation;
+    EXPECT_TRUE(fillFrames(s_animation, false));
+
+    string output = cv::tempfile(GetParam().c_str());
+    ASSERT_TRUE(imwritemulti(output, s_animation.frames));
+    vector<Mat> read_frames;
+    ASSERT_TRUE(imreadmulti(output, read_frames, IMREAD_UNCHANGED));
+
+    {
+        ImageCollection collection(output, IMREAD_UNCHANGED);
+        EXPECT_EQ(read_frames.size(), collection.size());
+        int i = 0;
+        for (auto&& frame : collection)
+        {
+            EXPECT_EQ(0, cvtest::norm(frame, read_frames[i], NORM_INF));
+            ++i;
+        }
+    }
+    EXPECT_EQ(0, remove(output.c_str()));
+}
+
+INSTANTIATE_TEST_CASE_P(/**/,
+    Imgcodecs_ImageCollection,
+    testing::ValuesIn(exts_multi));
+
 #endif // HAVE_PNG
 
 }} // namespace